Tire pressure change

[Coyote Chris]

I am curious as to what you all think a detectable tire pressure change is for the common good rider. Not a road racer....US...you and me. Specifically, how much would the tire pressure have to drop before you would say to yourself, somethings not right here....
2 lbs? 4 lb? 6 lbs? 8 lbs. NOne of the above.

I will save my opinions on David Moss.

 

[Phil Tarman]

I'm guessing it would be over 10 pounds before I'd notice. Maybe more than that.

 

[Macka]

I may be more sensitive, as a mechanic, than most but I can feel a difference in steering and or handling with a drop of 3 or 4 psi.
I have been using a TPMS for 3 or 4 years now and would not be without one on any vehicle that I own.
Using it (the TPMS) is an education really.
It is surprising how quickly the tyre pressure and temperature, particularly the rear, rise in hot weather.
With the rear starting out at 41psi at 15C ambient, I have seen over 55psi and over 50C tyre temperature at 40+C ambient.

Macka

 

[silshooter]

Working on the shops (1970's/80's), it was rare to find a bike with proper tire pressures.

 

[Phil Tarman]

Since I got my current TPM, I've been like Macka -- amazed at how quickly pressures come up when I start moving. I've also been surprised that the front tire doesn't seem to heat up much (at least with the kind of riding I've done) at all. Sometimes it's just a little dab over ambient air temperature. The rear runs a few degrees hotter than the front. So far, I've seen rear tire pressure go up to 48-49psi after starting at 42.

 

[ARKNT]

I would probably not notice tire pressure changes until about 8 psi or so. That probably depends on the type of riding I'm doing at the time (curves, straight).

It doesn't surprise me that the rear pressure goes up quite a bit. The temps get pretty warm for a tire when you are located behind the hot engine, exhaust, and running on hot black asphalt that in summer here would burn your feet if not protected by shoes.
I once thought the NT rear drive might have issues because it was pretty warm. It was just all that ambient heat warming it up.

Brad

 

[Coyote Chris]

Personally, with modern tires, I doubt very seriously if I could detect in a blind test any change under 5 psi. If we were all at a track, took a lap, and lowered out PSI 5 lbs, then went out again we might notice it. OTOH if we lost 5 psi due to a slow leak, I dont think we would notice the difference.

 

[Coyote Chris]

I am confused about TPMS. All cars after 2007 have it. but this guy wants us to believe its a inside sensor and not a function of the anti lock breaking system counting wheel rotations? How come my 2006 Maxtrix has it and the sensors have never stopped working if he is right?

 

[Phil Tarman]

Chris, I can guarantee that none of the TPM systems I've had on my motorcycles has had it tethered to either the ABS or to an inside sensor. Mine have had sensors that replaced the valve caps.

 

[Rand soper]

I know that on our Ford Fusion and BMW Z4 and Prius, there is a sensor that is part of the valve stem assembly. Every time the tires are replaced, they are serviced, which I assume means replacing the battery. I understand that there is also a system that uses the anti lock system to measure rotational speed of the tires to determine if there is low pressure.

 

[seagrass]

TPMS is done in one of two ways. Wheel rotation difference (using ABS system) and pressure sensors which are typically in the valve stem and have a battery.

TPMS is still not mandatory in many parts of the world including Australia.

Seagrass

 

[Phil Tarman]

I had never really thought about how tire pressures were monitored if there wasn't a wheel sensor. Wheel rotation difference makes a lot of sense. I guess it wouldn't work on some of the high performance cars that have different wheel sized front and rear. Or maybe the computer's smart enough to figure that stuff out.

 

[junglejim]

I don't have any psi numbers to state, but In general I think I'd notice a decrease in inflation before an increase. We are accustomed to our motorcycles warming up as we start out, including tire pressure.

I can remember detecting a slow leak a couple times when I noticed slow and mushy handling.

I'd expect the rear tire to run warmer than the front as stated above. First it carries more load. Secondly it is propelling the motorcycle. And as mentioned it is behind the engine and near the exhaust. I suspect you could cause the front tire to warm up more by doing some hard cornering and braking.

 

[Macka]

As stated above by seagrass, TPMS are not yet mandatory in Oz.
On the road is is not uncommon to see someone driving on a half flat tyre and not realise it.
In the old days, before the mid 70s, if you had a half flat tyre on the front of a car it would pull to that side.
With the introduction of "negative scrub radius" suspension, that changed as it was designed to prevent exactly that situation.

The systems that use wheel rotation speed through the ABS can be prone to errors and often will not respond until the tyre is half flat if the car is driven locally around many turns. It needs some straight ahead driving to evaluate the relative rotational speeds.
As a mechanic, I often have to re calibrate the system after doing a service which involves adjusting tyre pressure, rotating the wheels or replacing the tyres. It is important that all four tyres have approximately even wear and are of similar (preferably the same) construction/model.
If you have two new tyres on the front and very worn ones on the rear it may give false indications.
Even worse, you must not have a new tyre and a very worn tyre on the same axle.
Regular wheel rotation to promote even wear is the best way.
The TPMS on my Honda has saved me from being stranded in the middle of nowhere twice. I will never ride without it again.
I have had three punctures on the Honda, all in the rear. Only one was in a populated area.

Macka

 

[mikesim]

I usually adjust my TP's if they deviate more than about 2psi from setpoint. Unless I can attribute them to a temporary cold snap

 

[DirtFlier]

My bike's kit includes hand tools to remove either wheel, plug kit, and small compressor. I've had to use them several times on various trips, all of them far from home, and was glad I had them!

 

[mikesim]

I too would never be without a TPM system on my car or bike. One other thing to expand on what Macka posted about uneven tire wear. On some modern AWD systems driveline damage can occur if the tires are not worn relatively equally. Another good reason for periodic rotation. I do mine every 6K.

Mike

 

[Phil Tarman]

I've always carried tire plugs, (and since 2012 in Spearfish, gummy worms, too) and a gauge and mini-compressor. I had a flat at Perkins in Spearfish one morning. I think we ended up with 4 or 5 of the mushroom plugs inside the tire. Somebody went to K-Mart across the parking lot and bought gummy worms and they held long enough to get back to the City Campground [BTW, I don't know if I mentioned it or not, but I loved the City Campground!]. The tire was flat within a few minutes of getting there, and I ended up being towed to the Honda dealer in Rapid City and bought a tire. We didn't get there until just a few minutes before closing, so I rode back to Spearfish with the tow truck driver. Somebody (sorry, guys, but I can't remember who) gave me ride back to Rapid City the next morning and I had to hang around and wait for several hours.

I have plugged tires for two of my Concours buddies and those plugs lasted. The Stop'n'Plug (is that there name?) guy at the IMSA motorcycle show in Denver this year told me that our problem was that we didn't pull the plugs back against the mushroom as we put air into the tire. He said not to cut the part that's left sticking out until you've got the tire inflate.

 

[Macka]

At the same time as fitting the TPMS to my NT I also fitted metal (chromed) "T" valves.
This means that I don't have to remove the Sensors to top up the pressure.
I prefer to use external sensors, especially on bikes, as it easy to damage the internal ones when removing the tyre to replace the battery or tyre.

Macka

 

[mikesim]

On cars, it is an inside sensor. I've seen it. Had to have a few changed - they last about three years, then the battery goes bad.

I've never had one on a cycle. I'd looked, a long time ago...maybe ten years ago...what they had were gizmos that fit over the valve stem. I passed. May have to revisit that.

My first TPMS on Traveller was an internal system made by Orange Electronics. I loved it! Not only did it read tire pressure it also had an internal thermistor which read tire temperature, The sensors lasted thru two tire changes so when the time came to replace the tires again, I tried to be proactive and put new sensors in while the tires were changed. I ordered new sensors from the US distributors for Orange. When I received them I noticed that the manufacturing date code was about three years previous. I contacted Orange and they advised that since they were never installed the batteries would still be fresh. I was dubious, but what the hell! I installed 'em with the new tires and life was good for about a year and then the front sensor failed followed shortly by the rear. I contacted the Orange US distributor and never received a reply, the toll free number was disconnected. I emailed Orange in Taiwan and after several weeks received a reply. They kindly advised that they were looking for a new US distributor but in the meantime would send me a complete new system gratis. By that time, not wanting to be without a TPMS I installed a Hawk System which used external sensors. It worked great except the "weatherproof" receiver wasn't. After riding thru several rainstorms condensation developed internally on the display and sadly expired. It was then that I bought a Garmin Zumo which had an optional TPM system using the external sensors. The Zuma was pricey enough but the sensors were an additional $60 each! The neat thing about the Garmin system is that the sensors have replaceable batteries. I have replaced the batteries once and it is still working happily. One caution if anyone chooses this route is to use the proper battery. The manual says to only use Lithium "Bromide" batteries. The manual speaks truth as the plain old lithium batteries lose their potency in cold weather <35 degrees. I wouldn't shy away from a system merely because of the external sensors. One other caveat about the external sensors, and I'm sure Phil will vouch for my veracity on this. If you go the external sensor route, be sure to use metal valve stems! If you mount the external sensor on your OE rubber valve stem it will flex the stem eventually causing stem failure!! This is the voice of experience talking to you!

Mike